For current measurement in conductor systems measuring current transformers are known in which the current-carrying conductor to be measured is passed through a cable duct of the measuring current transformer in the form of a primary winding, and in the secondary winding of the measuring current transformer generates a measuring signal that is proportional to said primary current that can be analysed and which can be fed to an analysing device, for instance a conventional current measuring device, for displaying or to an analysing device for further digital signal processing. Such measuring current transformers are employed in electrical protection devices for fault current measurement (differential current measurement) in earthed (TN) networks, for test current measurement in connection with insulation fault localization devices in unearthed (IT) networks and independently of the type of network in devices for load-current measurement.
The devices for fault, test and load current measurement are frequently characterized by a spatially separated arrangement of the measuring current transformer and the signal-processing analysing device. Hence, from the prior art measuring devices for insulation fault localization are known, in which the measuring current transformers are arranged as separate units separately from the device which carries the electronics for processing the measuring signals delivered by the current measuring transformers. The connection between the individual measuring current transformers and the signal-processing device is generally produced by means of twisted cables. It is a disadvantage for installation in switch cabinets that arrangements of this type require much space as a consequence of the multiplicity of separately mounted measuring current transformers and the supply lines thereof, are confusing to some extent and are inflexible with regards to the installation position. The signal-processing device is fastened in a switch cabinet, for the most part on a top-hat rail, whereas the transformer elements are mounted via spacers or deep angle brackets in a plane lying there behind.
Likewise known are devices for locating insulation faults, in which the processing electronics and the measuring current transformers are combined in a device. A device of this type is disclosed in the laid-open specification DE 10 2005 054 544 A1.
This document describes an apparatus for locating insulation faults in unearthed AC voltage networks, in which a module consisting of a plurality of current transformers has a microprocessor with bus interface and this module is arranged via deep angle brackets in a second rear plane lowered between two top-hat rails in each case. In this case, the current transformers are arranged in two rows standing in an offset manner on a printed circuit (base) board of the module in such a manner that the cable openings of the current transformers are arranged pointing forwards at right angles to the top-hat rails in the mounted state of the module and the cables run vertically through the openings.
Although an extensive wiring is dispensed with in this apparatus due to the integration of the transformers, the installation options are also limited here, as an expedient mounting is only possible with deep angle brackets in a plane of the switch cabinet lying behind the top-hat rail.